冷媒R245faの水平平滑管内凝縮熱伝達および圧力損失-凝縮特性に及ぼす飽和温度の影響

抄録

This study experimentally investigates the condensation heat transfer and pressure drop characteristics inside a horizontal smooth tube containing R245fa, which is used as a working refrigerant for a high-temperature heat pump and binary generator. The test section is a 4m-long counter flow-type double pipe heat exchanger. In this section, the refrigerant flows through the inner test smooth tube, which is an 8.32mm inner diameter copper tube, and the heat source water flows in the annulus surrounding the inner tube. The annulus is divided into five subsections, each 557mm long. The condensation experiment is conducted under a mass velocity range of 50 to 300kg/(m²s) and saturation temperature range of 40°C and 60°C. The measured condensation heat transfer and frictional pressure drop characteristics of R245fa are clarified for the effects of mass velocity, vapor quality and saturation temperature. Furthermore, experimental results of condensation heat transfer coefficient and frictional pressure drop are compared with several previous correlations. The condensation heat transfer coefficient decreases with increasing saturation temperature, which is highly dependent on the flow patterns. Also the frictional pressure drop decreases with increasing saturation temperature, but it is less dependent on the flow patterns. In comparison with previous correlations for the condensation heat transfer coefficient, predicted results of Haraguchi et al., Cavallini et al. and Dobson - Chato are expected to be slightly smaller in conditions highly affected by forced convection. The experimentally determined frictional pressure drops are ±30% consistent with the predicted results of Haraguchi et al. and Miyara et al.